1. Field of the Invention
The present invention relates to a support structure of an optical part, and more specifically to a support structure of an optical part such as a mirror or a lens of a system for optically reading out recorded information.
2. Description of Background Information
In a system for optically reading out recorded information such as a video disc player system, an optical part such as a mirror is disposed in an optical path of a light beam for reading out information, so as to direct an incident light beam to the recording surface of a recording disc, or directing a reflection of the read out light beam from the recording surface of the recording disc. Generally, such a mirror is mounted to be rotated around an axis parallel to a radial direction of the recording disc, or parallel to a tangential direction of a recording track of the recording disc. Therefore, the rotation of the mirror around this axis causes a movement of the light spot on the recording surface of the recording disc. A tracking servo control or a tangential servo control is thus effected in accordance with the rotating movement of the mirror.
In this type of arrangement, generally, the mirror is supported on an elastic support member which allows the rotation of the mirror around the axis of the rotation. However, due to the elasticity of the elastic support member, the mirror is also slightly movable in a direction other than the axis of rotation, in a direction perpendicular to the axis of rotation, for example. This movement is especially notable around a resonance frequency which is present in a high frequency range.
Therefore, in operation, the mirror may be rotated around an axis perpendicular to the proper axis of rotation during the driving of the mirror in accordance with a servo operation. Generally, this undesirable rotation of the mirror is a result of an error of the direction of the driving of the mirror, or unbalanced distribution of the mirror weight. If we assume that the mirror is utilized as a tracking mirror of a tracking servo system, the mirror is likely to rotate also along a tangential direction of the recording track, and such a tangential movement of the mirror will cause an external disturbance to the operation of a tangential servo system which is used for time axis correction. Further, if the frequency of the tangential movement of mirror is out of the range of the tangential servo control, it is difficult to compensate for the error of the time axis caused by the tracking servo control.